1. Field of the Invention
The present invention relates to a weighing method and to a device for weighing mobile objects, such as goods vehicles designed for road or rail-bound traffic.
2. Description of the Background Art
To weigh moving objects, for instance goods vehicles, weighing devices comprising a large-size weighing machine traditionally are used, onto which the entire vehicles may be driven, come to a standstill and be weighed to be thereafter driven off. The disadvantages inherent in this common type of vehicle weighing machines are, above all, their dimensions. The weighing machine must have a length of 24 meter and a weighing capacity of up to 80 tons, which makes the weighing machine space-requiring, difficult to transport/mount, and expensive to manufacture and to service. In addition, it is awkward to check that the entire vehicle is actually positioned on the weighing machine during the weighing process.
Another type of weighing machine in use is a smaller weighing machine, the axle load meter, according to which the vehicle is driven continuously across the weighing machine. Each axle is weighed separately on the weighing machine. The total weight is then calculated by adding together the individual axle weight measurements. The disadvantage found with this type of vehicle weighing machine is, however, the sensitivity of the weighing machine to unevenness in the ground ahead of and after the weighing machine, since differences in height and resistance to rolling affect the axle load with respect to the axle present on the weighing machine, a situation which consequently makes the measurement results less reliable.
With respect to both weighing devices above regulations prescribe that check weighing be performed annually, using certified calibrated weights up to the maximum capacity of the weighing machine. In the case of a static (full length) vehicle weighing machine, this means 80 tons whereas in the case of a dynamic axle load meter a capacity of 15 tons suffices. Certification of weighing machine accuracy is a costly and time-consuming enterprise involving fork-lift trucks, freights and a verification controller authorised by the appropriate agency. For obvious reasons, accuracy certification of full-length weighing machines must always be performed in situ whereas axle load meters may be transported to the accuracy testing authority and the customer consequently may replace the weighing machine to be tested by a recently certified weighing machine, in accordance with a replacement system.
Should the weighing machine brake down during the duration of the period of certification, the certificate of weighing machine accuracy becomes invalid, and this goes for both types of weighing machines, and a new certification process must be initiated.
In addition, it may be difficult to know whether the results provided by the weighing machine are accurate or not. Snow, grit or the like underneath the weighing machine may affect the weighing machine so as to distort the weighing results. This is especially serious in connection with the type of weighing machines that measure the weight, axle by axle, since any system error in this case is multiplied by the number of axles involved.